The present invention relates to a continuous process for cleaning and preparing grossly soiled products of plastic material, such as sheets, bands, sacks or the like for subsequent re-use of the plastic material, in which the plastic material after removing rough foreign objects therefrom is comminuted and fed into an extruder.
Such processes have become important in recent times, due to the increasing shortage and cost of raw materials as well as in consideration of the evironment, to prevent such plastic products after use of the same to form part of an ever increasing amount of garbage which has to be dumped or burned.
During the production of, for instance, sheets or bands of plastic material, there will result a certain percentage of clean dry scrap which, separated in accordance with its composition, may be comminuted and without further treatment fed into an extruder. Such scrap constitutes about 10% of the material necessary for producing the aforementioned or like products. 90% of the material is transformed into products for instance sheets or bands which are mainly used in the packaging industry. Plastic material used for the packaging industry are usually discarded after a relatively short time and such discarded plastic material are, at least partly, considerably soiled.
Attempts have already been made to clean and prepare such soiled products of plastic material which have been used for the same purpose, for instance as sacks for fertilizers, which accumulate after use in considerable amounts, in order to remove from such products foreign particles clinging thereto as for instance fertilizer particles, humus particles, sand, etc.
For this purpose it is known to free the solid products of plastic material from foreign particles, to subsequently comminute the products in a cutting mill and to feed them thereafter into a special regranulating extruder.
This known process has the disadvantage that fine grained foreign particles will cling, even after the comminuting of the plastic products to the latter and be thus fed with the comminuted plastic material into the extruder. This will result in clogging the sieves of the extruder as well as in an increased wear of the various parts thereof, and the necessity to exchange the clogged extruder sieves, which evidently will reduce the output of the extruder. In addition, very fine grained foreign particles will not be retained by the sieves of the extruder and thus be included in the end product produced so that such end product will be of inferior quality.